Polyoxyethylene-base nonionic surfactants have high detergency and can also be used favorably in a state combined with other ionic surfactant, so that various combinations thereof with other surfactants have been proposed. In particular, many surfactant compositions comprising such nonionic surfactants and anionic surfactants have been disclosed owing to their excellent detergency. Such surfactant compositions are used mainly as detergent in a state diluted with a diluent such as water.
It is well known that when a nonionic or anionic surfactant is mixed with water in a high concentration, the resulting mixture exhibits a viscosity higher than that of the surfactant itself by ten or more times. In particular, when an anionic surfactant is mixed with water, the resulting mixture exhibits remarkably high viscosity over a wide concentration range to result in difficult handling. Therefore, an anionic surfactant is generally handled as a low-concentration aqueous solution. Economically, it is desirable that a detergent containing a surfactant is free from extra liquid components as far as possible. However, the concentration of a detergent containing an anionic surfactant for useful handling is limited up to about 30 wt %. A composition having a concentration of 50 wt. % or above could little be lowered in the viscosity even by the addition of a diluent such as water, being difficult to handle by the use of a conventional container such as a can or a drum.
In order to solve such a problem, aliphatic alcohols and adducts thereof with alkylene oxides have been proposed in JP-B-6-76594 as viscosity modifier. However, an aqueous surfactant solution containing such an alcohol or adduct still exhibits a viscosity of the order of 10000 cP at 70.degree. C., not permitting easy handling at ordinary temperatures. Further, JP-A-53-58508 has proposed a liquid detergent excellent in fluidity which comprises a polyoxypropylene polyoxyethylene alkyl ether and a polyoxyethylene alkyl ether sulfate, but is silent on the viscosity of the detergent in a high concentration range. Further, an attempt was made to lower the viscosity by the addition of a solubilizing agent. Although the addition of a solubilizing agent gives a remarkable viscosity reducing effect, the addition of some solubilizing agent in a large amount is liable to bring about flammability unfavorably.
Further, EP-A 58139 discloses the treatment of a fabric with both (A) an anionic surfactant and (B) a nonionic block copolymer comprising ethylene oxide units and propylene oxide units, but is silent on the behavior of high-concentration compositions thereof.
As described above, there has not been found as yet any surfactant composition which contains an anionic surfactant and exhibits excellent handleability even in a high surfactant concentration range. Under these circumstance, it has been expected to develop a high-concentration surfactant composition which contains an anionic surfactant and is easily handleable at room temperature.